What is an osteoc last?

• A. Cell that destroys bone
• B. Cell that builds bone
• C. Cartilage-forming cell
• D. Bone-maintaining cell

Answer: (A)

Osteoclasts are the bone-resorbing cells in bone remodeling. They originate from the monocyte/macrophage lineage and fuse to form multinucleated cells that attach to the bone surface. In a sealed resorption pit, they secrete acids to dissolve mineral and proteolytic enzymes like cathepsin K to break down the organic matrix, effectively destroying old or damaged bone so osteoblasts can lay down new bone. This resorption is tightly regulated by signals such as RANKL promoting osteoclast formation and activity, with calcitonin inhibiting them. So the term describes a cell that destroys bone, rather than building bone, forming cartilage, or simply maintaining it.